Method of producing a plastic moulded part including an external covering

ABSTRACT

The present invention is a mould and a method of moulding a plastic component using the mould that enable the manufacturer of a moulded component ( 45 ) which has an external covering. The method of moulding comprises either locating a pre-formed component ( 41 ) into a first part of the mould or vacuum forming a thin film ( 40 ) into a mould cavity. A first mould part ( 15 ) has a mould cavity into which the pre-formed component ( 41 ) is placed or the thin film ( 40 ) is vacuumed formed into. The method continues by partly closing a second part of the mould ( 25 ) into the first part of the mould ( 15 ) and injecting molten plastic ( 34 ) onto the surface of the pre-formed component ( 41 ) or thin film ( 40 ). The second mould part ( 25 ) is then fully closed to force the molten plastic ( 34 ) to fill the resultant mould cavity ( 36 ). This bonds the molten plastic to either the pre-formed component ( 41 ) or the thin film ( 40 ) to form the final shape of the moulded component ( 45 ). Just prior to the mould parts ( 15 ) and ( 25 ) closing, a cutting edge ( 28 ) abuts against and cuts either the pre-formed component ( 41 ) or the thin film ( 40 ). This trimming occurs around the periphery of the cutting edge ( 28 ). The moulded component ( 45 ) is then ejected by opening of the mould parts ( 15 ) and ( 25 ). This process enables the production of a moulded component ( 45 ) with an external covering.

BACKGROUND OF THE INVENTION

Moulding, and in particular injection moulding, is used in manyapplications to mass produce plastics components at low unit cost. Acharacteristic of the conventional injection moulding process is that,because only one plastics material is injected into the mould, theresultant component has relatively uniform properties throughout. Inapplications where different material properties are required fordifferent areas of a component, this can produce difficulties and/orresult in the need for further steps to produce a final product. Forinstance, in many applications it is desirable to change the surfacecharacteristics of a plastics component produced by injection moulding(to provide hardness, colour, reflectivity etc.).

One way of changing the surface properties of a part produced byinjection moulding is to cover (partially or fully) that part with afilm. Such a film may add abrasion resistance, colour, or reflectivityfor instance.

The addition of a film after the injection moulding process adds costand complexity to the production of plastics moulded parts having a filmcovering.

By way of example, it is known to apply thin plastic film to a vehicleexternal mirror housing to provide colour matching to that of the bodyof the vehicle and to add abrasion resistance. Known techniques for suchapplication add complexity to the production of mirror housings.

It is an object of the present invention to provide an improved methodof producing a plastics moulded part having an external covering.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a method of moulding aplastic component comprises locating a first pre-formed component into afirst part of a mould having at least two components that, when closed,form a mould cavity, partly closing said mould, injecting molten plasticinto said mould cavity on one side of said pre-formed component, andclosing said mould to force said molten plastic to fill said mouldcavity and to bond to said one side of said pre-formed component, onepart of said mould having a cutting edge that engages against and trimssaid pre-formed component around said cutting edge upon closure of saidmould components.

Preferably the pre-formed component is a generally concave componentwhich may have a thin wall. The section of the peripheral edge of thepre-formed component may be curved inwardly towards the centre of thecomponent. The cutting action of the mould parts trim the peripheraledge of the preformed component adjacent the inwardly curved sectionflush with the plastic which is moulded onto the internal surface of thepreformed component. This enables a component to be moulded that has asmooth and uninterrupted surface to the point where the trimming occurs.

In the case of a pre-formed component where the peripheral edge curvesin towards the centre of the part, this will obviously result in anundercut surface which is located between the outer edge of thepre-formed component and the edge where the trimming of the pre-formedcomponent occurs. In order to ensure that such component can be releasedfrom the various mould parts, an intermediate or third mould part can belocated between the first female and second male parts of the mould.This intermediate part will have an aperture through which the malecomponent locates. Also, it is provided with an undercut recess againstwhich the inwardly curved peripheral edge of the pre-formed componentlocates. Separation of the female and intermediate parts will thenenable release of the finished moulded component.

Preferably, the pre-formed component is sufficiently resilient to enableit to be located within the cavity formed by both the first andintermediate mould parts. The peripheral edge of the pre-formedcomponent extends beyond the undercut recess so that it overlies theregion against which the cutting edge abuts. Preferably, the cuttingedge abuts the intermediate mould part close to the end of the undercutrecess.

The moulding technique relies on injecting the required amount of moltenplastic into the mould cavity prior to final closure of the mould parts.Once this occurs, sufficient closing pressure is applied to ensure thatthe molten plastic forms fully into the mould cavity as the componentsclose. Just prior to final closure of the mould parts, the cutting edgeabuts against the pre-formed component. Continued closure results in thecutting edge continuing to press into the pre-formed component until thecutting edge finally abuts against another surface of an adjacent mouldpart. This results in the preformed component being trimmed around thecutting edge.

In addition to a method of moulding a plastic component, the inventionaccording to its first aspect also comprises a mould for moulding theplastic component comprising a first part of a mould having a cavityinto which a pre-formed component is located, a second part of saidmould that locates into the cavity of said first part and forms a mouldcavity between said second part and said pre-formed component, and acutting edge on at least one of said parts of said mould that engagesagainst and trims said pre-formed component around said cutting edgeupon closure of said mould components wherein said mould parts arepartly closed prior to molten plastic being injected into said mouldcavity on one side of said preformed component and then fully closed toforce said molten plastic to fill said mould cavity and to trim saidpre-formed component.

In a further aspect of the invention, a method of moulding a plasticcomponent in a mould having at least a male and female mould parts thatform a mould cavity when said mould is closed, comprises locating asoftened film of plastic over the recess of the female part of saidmould, drawing a vacuum within the recess of said female part of saidmould that causes said film of plastic to be vacuum formed onto thesurface of said female part of said mould, partly closing said mould,injecting molten plastic into said mould cavity on one side of saidplastic film, and closing said mould to force said molten plastic tofill said mould cavity and to bond to said one side of said plasticfilm, one of said mould parts having a cutting edge against whichanother part of said mould locates so that the cutting edge trims saidplastic film around said cutting edge upon closure of said mould parts.

Preferably, the method further comprises an intermediate mould part thathas surfaces defining an aperture through which the male mould partlocates and an undercut recess that locates adjacent the opening of thefemale mould part when the intermediate mould part is closed against thefemale mould part. In this case, the vacuum forming of the plastic filmresults in the film abutting against the aperture and undercut recess ofthe intermediate mould part.

In relation to all aspects of the invention, two halves of the mould mayeach have a cutting edge that engage upon closure of the halves. Thecutting edges may act to cut a pre-formed or vacuum moulded component bythe cutting edges moving past one another.

A still further aspect of the invention may also comprise a mould formoulding a plastic component comprising a first part of a mould having acavity into which a pre-formed component is located, a second part ofsaid mould that locates into the cavity of said first part and forms amould cavity between said second part and said pre-formed component, anda cutting edge on said first and second mould parts that trim saidpre-formed components around said cutting edges when said cutting edgesengage upon closing of said first and second mould parts, wherein saidmould parts are partly closed prior to molten plastic being injectedinto said mould cavity on one side of said pre-formed component and thenfully closed to force said molten plastic to fill said mould cavity andto trim said pre-formed component.

In addition to the moulding process which is used in all of theabovementioned aspects of the invention, where a predetermined amount ofmolten plastic is injected into a mould cavity when the mould parts arepartially closed, the invention may also comprise a method of mouldingand mould parts that involve injection of molten plastic when the mouldparts are fully closed. This would result in the cutting edge trimmingthe pre-formed component or vacuum formed film prior to injection ofmolten plastic into the mould cavity.

Specific embodiments of the invention will now be described in somefurther detail with reference to and as illustrated in the accompanyingfigures. These embodiments are illustrative, and are not meant to berestrictive of the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred method according to the invention is illustrated in theaccompanying representations in which:

FIG. 1 shows a cross-sectional view of a three-part mould suitable forproducing a moulded component having a thin film covering;

FIGS. 2 to 7 show cross-sectional views of the three-part die of FIG. 1in progressive positions for producing a moulded component having a thinfilm covering;

FIG. 8 shows a cross-sectional view of a two-part mould for producing amoulded component having a thin film covering;

FIG. 9 shows a cross-sectional view of a two part mould for producing amoulded component having a thin film covering using a pre-formedcomponent inserted into the mould cavity; and

FIG. 10 shows a part-sectional view of a pair of cutting edges.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a three-part mould comprising a female mould part 15, anintermediate mould part 20 and a male mould part 25. A conduit 27 isprovided in the male part 25 to allow molten plastic to be injected intothe mould cavity which is formed when the male mould 25 is inserted intothe female mould part 15. FIG. 1 shows a vacuum conduit 17 communicatingwith a groove 18 which extends around the periphery of the cavity withinthe female mould part 15. The intermediate mould part 20 has a groove 22within which a compressible seal 30 locates. The compressible seal 30provides an airtight seal between the intermediate mould part 20 and thefemale mould part 15. This seal and the vacuum conduit 17 enable air tobe evacuated from the mould cavity.

In this method of moulding a thin film 40 is placed against theintermediate mould part 20. The thin film 40 is heated to enable it tovacuum form into the female mould part 15. This is achieved byevacuating the air within the mould cavity by vacuum conduit 17 once theseal 30 is formed between the female mould and intermediate mould parts15 and 20. The vacuum forming of the thin film 40 is shown at FIG. 2.The peripheral edge of the thin film 40 may be held with respect to theintermediate mould part 20 during the vacuum forming process.

The intermediate mould part 20 comprises an aperture 21 through whichthe male mould part locates. The aperture 21 is formed by a firstsurface 23 and a second surface which comprises an undercut recess 24.The term undercut is used as it describes a moulding surface having alarger diameter or undercut in relation to the minimum diameter of theaperture 21. In other words, a component formed within the cavitydefined by the cavity within the female mould part and the undercutrecess 24 of the intermediate mould part 20 could not be released fromthe mould cavity if the female and intermediate mould parts 15 and 20are held together because of the portion formed on the moulded articleby the undercut recess 24.

The male mould part 25 is provided with a cutting edge 28. In thisembodiment, the cutting edge 28 extends around the periphery of the malemould part 25. Due to the taper of the first surface 23, the cuttingedge 28 does not abut against the surface until the male mould part 25is fully engaged with the other mould components 15 and 20. The cuttingedge 28 abuts against and cuts through the thin film 40 which ispositioned over the first surface 23 after the vacuum forming process.This has the effect of trimming the thin film 40 during the mouldingprocess.

FIGS. 1 to 7 show the operation of the various mould components toproduce a plastic component 45. The first stage of the process is shownin FIG. 1. In this stage, the female and intermediate mould parts 15 and20 are held together. A heated thin film 40 is located over the aperture21 and held in place. A vacuum is then applied by a vacuum conduit 17 toevacuate air from the mould cavity. This results in the thin film 40forming into the mould cavity as shown in FIG. 2.

In the next step (FIG. 3) the male mould part 25 is partially insertedinto the female mould part 15 through the aperture 21. This results in afirst mould cavity 35 being formed between the thin film 40 and the malemould part 25.

As shown in FIG. 4, a predetermined amount of molten plastic 34 isinjected into the mould cavity 35 via conduit 27. The amount of moltenplastic injected into the first mould cavity 35 is sufficient to fillthe resultant mould cavity 36 when the mould component is fully closed.

Once the required amount of molten plastic is injected into the firstmould cavity 35, the male mould part 25 fully closes with respect to themould parts 15 and 20. This is shown in FIG. 5. The male mould component25 is used to compress the molten plastic 34 into the resultant mouldcavity 36. In this process, the molten plastic is bonded and formedagainst the thin film 40. Bonding between the thin film 40 and themolten plastic results.

Just prior to the mould parts being fully closed, the cutting edge 28abuts against the thin film 40 so that further insertion of the malemould part 25 results in the thin film 40 being cut around the peripheryof the cutting edge 28. In this embodiment, the trimming of the thinfilm via the cutting action of cutting edge 28 occurs adjacent to theend of the undercut recess 24. This results in the thin film 40 beingtrimmed at a diameter which is smaller than the maximum diameter of theresulting component. The resultant mould cavity 36 tapers towards thepoint at which the thin film 40 is trimmed.

The ejection of the moulded component 45 is shown in FIGS. 6 and 7.First, the female mould part 15 is moved away from the moulded component45. The male mould part 25 is then moved away from the intermediatemould part 20 whereupon the moulded component 45 can be ejected.

This moulding process enables a thin film covering to be formed on amoulded component 45. This covering is achieved within the one set ofmould components and can result in the film covering peripheral edges ofthe moulded component which curve inwardly. The covering of suchundercut surfaces would not be possible in a conventional two-partmould.

The thin film 40 may comprise a laminate having a clear abrasionresistant outer layer, a coloured middle layer and an inner layer ofmaterial that will readily bond to molten plastics. Suitable materialsfor the inner layer would include ABS and ASA plastics. These sameplastics could then be used in a molten state to ensure bonding with theinner layer of the thin film 40.

In another embodiment of the invention, the same mould components shownin FIGS. 1 to 7 could be used with a pre-formed moulded component.Instead of vacuum forming a thin film 40, a pre-formed component usingeither vacuum forming or injection moulding could be inserted into themould cavity formed between the female and intermediate mould parts 15and 20 shown in FIGS. 1 and 2. Provided that the pre-formed componentwas sufficiently resilient or thin, then it could be inserted throughthe aperture 21. This insertion would readily occur even if thepre-formed component had a surface which located within the undercutrecess 24. The moulding process could also occur with a pre-formedcomponent 41 that did not have an inwardly curved surface and thattherefore did not require either an intermediate mould part 20 with anundercut recess 24. This is illustrated in FIG. 9. In this embodiment,the pre-formed component 41 would still be trimmed upon final closure ofthe mould part as illustrated in FIG. 5.

In a further embodiment as illustrated in FIG. 8 the vacuum formingprocess could be used in a mould that comprised only a female and malemould part 15 and 25. In this case, the vacuum conduit 17 would openinto the mould cavity of the female mould part 15 in order to vacuumform the thin film 40. Again, trimming the thin film 40 would occur at apoint at which the male and female mould parts 15 and 25 are fullyclosed. In this case, the cutting edge 28 will abut against the internalsurface of the mould cavity of the female mould part 15 and thereby trimthe thin film 40.

In addition to the cutting edge 28 described in the above embodiments, apair of cutting edges 28 may be used on two of the mould parts. As shownin FIG. 10, these cutting edges 28 may either abut to trim either apre-formed component or the thin film or alternatively may pass oneanother as shown in FIG. 10 so as to produce a cutting action fortrimming the thin film 40 or pre-formed component 41.

While the present invention has been described in terms of preferredmethods in order to facilitate their understanding of the invention, itshould be appreciated that various modifications could be made to theembodiments without departing from the principles of the invention.Therefore, the invention should be understood to include all suchmodifications within its scope.

1. A method of moulding a plastic part comprising: locating a pre-formedmaterial into a first part of a mould having at least two mouldcomponents that, when closed, form a mould cavity, wherein, an undercutrecess is formed on the surface of one of said at least two mouldcomponents, partly closing said mould, injecting molten plastic intosaid mould cavity on one side of said pre-formed material, and closingsaid mould to force said molten plastic to fill said mould cavity and tobond to said one side of said pre-formed material, one part of saidmould having a cutting edge that engages against and trims saidpre-formed material around said cutting edge upon closure of said atleast two mould components.
 2. A method of moulding according to claim 1wherein said pre-formed material is a generally concave thin walledcomponent with a peripheral edge curved inwardly toward the center ofsaid pre-formed material, said cutting edge trimming said peripheraledge flush with the plastic moulded on the internal surface of saidpre-formed material.
 3. A method of moulding according to claim 2wherein said mould comprises a first female part, a second male part andan intermediate part that has a surface defining: (i) an aperturethrough which said male part locates and (ii) said undercut recess abutsagainst said inwardly curved peripheral edge of said pre-formedmaterial.
 4. A method of moulding according to claim 3 wherein saidcutting edge abuts against a surface defining said aperture adjacentsaid undercut recess.
 5. A method of moulding a plastic part in a mouldhaving at least a male mould part, a female mould part, and anintermediate mould part, wherein said male mould part locates withinsaid female mould part to form a mould cavity when said mould is closed,said intermediate mould part has a surface defining: (i) an aperturethrough which said male mould part locates and (ii) an undercut recessthat locates adjacent the opening of said female mould part when saidintermediate mould part is closed against said female mould part,comprising: locating a softened film of plastic over the recess of thefemale mould part, drawing a vacuum within the recess of said femalemould part that causes said film of plastic to be vacuum formed onto thesurface of said female mould part, partly closing said mould, injectingmolten plastic into said mould cavity on one side of said plastic film,and closing said mould to force said molten plastic to fill said mouldcavity and to bond to said one side of said plastic film, one of saidmould parts having a cutting edge against which another part of saidmould locates so that the cutting edge trims said plastic film aroundsaid cutting edge upon closure of said mould parts.
 6. A method ofmoulding according to claim 5 wherein said cutting edge abuts againstsaid surface defining said aperture adjacent said undercut recess.
 7. Amethod of moulding a plastic part comprising: placing a first pre-formedmaterial into a first half of a two part mould, partly closing said twohalves of said mould, injecting molten plastic into said mould cavity onone side of said pre-formed material, and closing said two halves ofsaid mould to force said molten plastic to fill said mould cavity and tobond to said pre-formed material, said two halves of said mould eachhaving cutting edges that engage upon closing of said halves to trimsaid pre-formed material to a required size, wherein the surface of saidfirst half of said two part mould has an undercut recess.
 8. A methodaccording to claim 7 wherein said cutting edges act to cut saidpre-formed material by said cutting edges moving past one another.
 9. Amethod of moulding a plastic part comprising: locating a firstpre-formed material into a first part of a mould having at least twoparts that, when closed, form a mould cavity, wherein the surface ofsaid first part of said mould has an undercut recess, and closing saidmould and injecting molten plastic to fill said mould cavity and to bondto said one side of said pre-formed material, one part of said mouldhaving a cutting edge that engages against and trims said pre-formedmaterial around said cutting edge upon closure of said mould.
 10. Amethod of moulding a plastic part in a mould having at least a malemould part, a female mould part, and an intermediate mould part, whereinsaid male mould part locates within said female mould part to form amould cavity when said mould is closed, said intermediate mould part hasa surface defining: (i) an aperture through which said male mould partlocates and (ii) an undercut recess that locates adjacent the opening ofsaid female mould part when said intermediate mould part is closedagainst said female mould part comprising: locating a softened film ofplastic over the recess of the female part of said mould, drawing avacuum with in the recess of said female part of said mould that causessaid film of plastic to be vacuum formed onto the surface of said femalepart of said mould, and closing said mould and injecting molten plasticto fill said mould cavity and to bond to said one side of said plasticfilm, one of said mould parts having a cutting edge against whichanother part of said mould locates so that the cutting edge trims saidplastic film around said cutting edge upon closure of said mould parts.11. A mould for moulding a plastic part comprising: a first part of amould having a cavity into which a pre-formed material is located, asecond part of said mould that locates into the cavity of said firstpart and forms a mould cavity between said second part and saidpre-formed material, a third intermediate mould part that locatesbetween said first and second mould parts having a surface that defines:(i) an aperture through which said second part locates and (ii) anundercut recess that locates adjacent the opening of said first mouldpart when said intermediate mould part is closed against said firstmould part, and a cutting edge on at least one of said parts of saidmould that engages against and trims said pre-formed around said cuttingedge upon closure of said mould components wherein said mould parts areparty closed prior to molten plastic being injected into said mouldcavity on one side of said pre-formed material and then fully closed toforce said molten plastic to fill said mould cavity and to trim saidpre-formed material.
 12. A mould according to claim 11 wherein saidpreformed material is a generally concave thin walled material with aperipheral edge locating within said undercut when said intermediatemould part closes against said first mould part and said cutting edgetrimming said peripheral edge flush with the plastic moulded on theinternal surface of said pre-formed material.
 13. A mould according toclaim 11 wherein said cutting edge abuts against said surface definingsaid aperture adjacent said undercut recess.
 14. A mould for moulding aplastic part comprising: a first part of a mould having a cavity intowhich a pre-formed material is located, wherein the surface of saidfirst half of said two part mould has an undercut recess, a second partof said mould that locates into the cavity of said first part and formsa mould cavity between said second part and said pre-formed material,and a cutting edge on said first and second mould parts that trim saidpre-formed material around said cutting edges when said cutting edgesengage upon closing of said first and second mould parts, wherein saidmould parts are partly closed prior to molten plastic being injectedinto said mould cavity on one side of said pre-formed material and thenfully closed to force said molten plastic to fill said mould cavity andto trim said pre-formed material.
 15. A mould according to claim 14wherein said cutting edges act to cut said pre-formed material by saidcutting edges moving past one another.
 16. A mould for moulding aplastic part comprising: a first part of a mould having a cavity intowhich a pre-formed material is located, a second part of said mould thatlocates into the cavity of said first part and forms a mould cavitybetween said second part and said pre-formed material, a third part ofsaid mould that has a surface defining: (i) an aperture through whichsaid second part locates (ii) an undercut recess that locates adjacentsaid cavity of said first part when said third part is closed againstsaid first part of said mould; and a cutting edge on at least one ofsaid parts of said mould that engages against and trims said pre-formedmaterial around said cutting edge upon closure of said mould partswherein said mould parts are partly closed prior to molten plastic beinginjected into said mould cavity on one side of said pre-formed material.